The invention relates to the automatic shaping of a sheet or ribbon of fibres on a mould for the production of a range of articles such as aircraft wings, for example, from a composite strip consisting of glued or adhesive sized fibre elements, for example, glued or adhesive sized by impregnation with epoxy resin, which are precut to the required shape and dimensions and which are retained between two protective films as far as the place where they are engaged on the mould. As a rule, the top film consists of a paper strip having appropriate mechanical and chemical characteristics while the bottom film is a very thin film of plastics. The resulting composite strip, whose width is often between 25 and 150 mm and which is about 250 m long, is presented in the form of a reel with end plates of approximately 450 mm in diameter.
The technique resides in placing very accurately on the mould the precut and impregnated fibre elements carried along in the form of the composite strip referred to. The conventional apparatus e.g. as known from French Pat. No. 2,529,817 accordingly has a roller or similar pressure applicator for engaging the fibre strip on the mould, the top paper strip being recovered after passing below the applicator roller while the bottom protective film has of course been removed immediately before the fibres are pressed on to the mould.
There are a number of disadvantages inherent in using a roller of this kind for engaging the strip with the mould, whether it is unitary or in the form of a number of parts.
First, the paper tends to deviate laterally because of unevennesses in the mould surface, particularly if the surface is out of true, so tht appreciable random errors in the positioning of the precut fibre elements on the mould arise. Using a very flexible roller would not solve the problem.
This disadvantage seems unavoidable in the case of machines using a roller to apply the strip to the mould, for to prevent lateral deviations of the strip the same would have to be guided laterally in the immediate vicinity of the zone where the roller engages it with the fibres. Unfortunately, there is no possibility of providing a strip-guiding cheek projecting from the cylindrical surface of the roller at each of its two ends for the two cheeks would then bear on the mould and the roller could not perform its function of pressing the fibres on the mould. Conseqeently, the only way of guiding the strip is by elements disposed some distance from the fibre engagement zone; unfortunately this distance is excessive for satisfactory guiding of the strip because the applicator roller is already of a fairly substantial diameter and also because the reel from which the composite strip unwinds, and the reel on which the paper is wound after the fibres have been placed on the mould, are relatively distant from the fibre-engaging zone; these two reels cannot really therefore be expected to be of use as really efficient lateral guiding elements for the strip. This conventional general layout also limits apparatus performances since it means that the mould recesses cannot have a reduced radius of curvature.
Also, it has been found by experience that using an applicator roller leads to the formation of a "wave" on the fibres, with a resulting reduction in compacting quality, with repercussions on the characteristics of the end product.
The difficulties in placing the fibres satisfactorily on the relatively even surace of the mould arise mainly from the problem that the protective paper shifts at the place where the fibres are engaged on the mould.